1. Field of the Invention
The present invention relates to a wireless power storage device and a semiconductor device including the wireless power storage device. In particular, the invention relates to a wireless power storage device which transmits and receives data through electromagnetic waves and receives electrical power through electromagnetic waves, and to a semiconductor device including the same.
2. Description of the Related Art
In recent years, various electric appliances are coming into wide use, and a wide variety of products are being put on the market. In particular, the spread of portable wireless communication devices has been notable. As a power supply for driving a portable wireless communication device, a battery, which is a power receiving means, is built-in, and power is obtained from the battery. As a battery, a secondary cell such as a lithium ion battery or the like is used. As matters now stand, the battery is charged from an AC adaptor which is plugged into a household alternating current power supply, which is a power supply means (for example, see Reference 1: Japanese Published Patent Application No. 2005-150022).
Further, in recent years, individual identification technology which employs wireless communication which uses an electromagnetic field, radio waves, or the like has attracted attention as a mode of usage of wireless communication devices. In particular, an individual identification technology which employs an RFID (radio frequency identification) tag that communicates data via wireless communication, which is an example of a wireless communication device, has attracted attention. An RFID tag is also referred to as an IC (integrated circuit) tag, an IC chip, an RF tag, a wireless tag, and an electronic tag. Individual identification technology which employs RFID tags is beginning to be made use of in production, management, and the like of individual objects, and it is expected that this technology will also be applied to personal authentication, through inclusion in cards or the like.
RFID tags can be divided into two types, according to whether they have a built-in power supply or receive a power supply from outside: active type RFID tags, which can transmit an electromagnetic wave which contains information included in the RFID tag, and passive type RFID tags, which drive by converting an electromagnetic wave (a carrier wave) from outside into electrical power (regarding the active type, see Reference 2: Japanese Published Patent Application No. 2005-316724, and regarding the passive type, see Reference 3: Japanese Translation of PCT International Application No. 2006-503376). Active type RFID tags have a built-in power supply for driving the RFID tag, and include a battery as the power supply. Meanwhile, with passive type RFID tags, a power supply for driving the RFID tag is made by employing electrical power of an electromagnetic wave (a carrier wave) from outside. Passive type RFID tags have a structure which does not include a battery.